1. Field of the Invention
This invention relates to drug delivery systems.
More particularly, the invention relates to ambulatory hypodermic infusion pumps.
In a further and more specific aspect, the invention relates to high-output paraffin thermal elements for actuating various medical infusion pumps.
2. Background of the Invention
Within the art of infusion pump technology, various drive mechanisms have been developed for driving the lead screw or syringe piston of the infusion pump. A primary objective in the design of such mechanisms has been to make them compact and lightweight enough to be incorporated into the infusion pumps without seriously restricting the patient's freedom of movement, while still maintaining a high level of reliability and controlled, accurate delivery.
Among the various prior art mechanisms which have been proposed to meet this objective have been solenoid devices designed to create a pulsating pumping action. Other mechanisms utilize the force of tension springs. Still others use compressed gas as the driving force. Electric motors have also been used. One prior art device uses a latex bladder which has been prestressed to create a constant force and thus a constant infusion rate. While all of the above drive mechanisms provide novel and interesting solutions to some of the problems in making a compact, highly mobile infusion pump, none provide a complete system of solutions for all of the problems that arise under a variety of circumstances. For instance, most of the prior art drives are unable to ensure constant displacement regardless of force. Thus, variations in a patient's blood pressure, drops in fluid line pressure, and various other factors are likely to effect the flow rate of fluid being dispensed from the pump.
One type of mechanical force which has not, to date, been used for driving medical infusion systems is the force which can be derived from heat energy due to temperature changes. Devices for converting temperature changes into mechanical motion, often referred to as thermal actuators, are well known and are commonly found in such devices as fluid mixing valves, waterline thermostats, fire alarms and household zone valves.
One of the major problems in the design of prior art thermal actuators has been that the internal frictional forces have been high, leading to wear on the squeeze boot, loss of piston power, and large hysterisis. Since the frictional forces are proportional to the surface area of the actuator rod, one way of reducing these forces has been to limit the length of the actuator stroke. Consequently, actuators having strokes longer than 0.4" are not commercially available. Similarly, since both the external force and the frictional force on the rod increase as the square of the diameter of the rod, small diameter (i.e. less than 0.125"), and hence, low output rods are also not available.
Still another problem of prior art actuators has been that it is not possible to repeatedly adjust the activation temperature of the thermal actuator after fabrication.
Another shortcoming of prior art thermal actuators has been the intrusion of outside materials into the interior of the boot. In the prior art, if the actuator is immersed in a pressurized fluid and left in the relaxed position for extended periods of time, the fluid can enter the space between the boot and the rod and shift the actuation temperature.
All of the above shortcomings have made prior art thermal actuators unsuitable for use in medical infusion pump technology, which requires a higher output, longer strokes, and greater reliability that the prior art devices are capable of delivering.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of this invention to provide high output, long stroke thermal actuators which are suitable for driving a variety of medical infusion pumps.
Another object of the invention is to provide a family of infusion pumps which are capable of utilizing several sources of power such as rechargeable and disposable batteries, as well as ambient and patient body heat.
And another object of the invention is to provide an infusion pump motor which can be used with a variety of syringe types including disposable syringes.
Still another object of the invention is to provide an infusion pump motor capable of producing constant displacement regardless of force.
Yet another object of the invention is to provide a family of infusion pumps, all significantly smaller than conventional units to allow increased patient comfort and ambulatory freedom.
Yet still another object of the invention is the provision of an infusion system having improved safety features such as an occlusion alarm and direct visual verification of drug delivery.
And a further object of the invention is to provide a highly reliable and accurate infusion pump at reduced manufacturing costs.
And still a further object of the invention is the provision of an infusion system having simple mechanical prime and purge functions.
And yet a further object of the invention is to provide a tamper-resistant infusion system.
And still a further object of the invention is the provision of a user-operable infusion system capable of slow and smooth activation.